Systems, methods, and devices for radiation beam asymmetry measurements using electronic portal imaging devices

Abstract

Systems and methods for determining beam asymmetry in a radiation treatment system using electronic portal imaging devices (EPIDs) without implementation of elaborate and complex EPID calibration procedures. The beam asymmetry is determined based on radiation scattered from different points in the radiation beam and measured with the same region of interest ROI of the EPID.

What is claimed is: 
     
       1. A system for determining radiation beam symmetry in a radiation device, comprising:
 an imaging device configured to measure radiation scattered from a first scatter aperture and a second scatter aperture generated in a radiation field of the radiation device, the first and second scatter apertures being symmetric to each other; and 
 a processor configured to calculate a beam asymmetry value based on the measured scattered radiation, 
 wherein the beam asymmetry value is calculated based on an amplitude of the scattered radiation from the first scatter aperture and an amplitude of the scattered radiation from the second scatter aperture. 
 
     
     
       2. The system of  claim 1 , wherein the first and second scatter apertures are generated using a collimator of the radiation device, the collimator being configured to rotate around a collimator rotation axis. 
     
     
       3. The system of  claim 2 , wherein the first and second scatter apertures are generated by creating an off-axis field using the collimator and rotating the collimator around the collimator rotation axis from a first collimator location to a second collimator location, the second collimator location being rotationally symmetric to the first collimator location. 
     
     
       4. The system of  claim 3 , wherein the off-axis field is generated by positioning at least an element of the collimator so as to be offset relative to the collimator rotation axis. 
     
     
       5. The system of  claim 4 , wherein the generated off-axis field is a 1-2 cm rectangular or square radiation field. 
     
     
       6. The system of  claim 3 , wherein the imaging device is an electronic portal dose imaging device (EPID), and the scattered radiation is measured using a plurality of pixels located in a region of interest ROI of the EPID. 
     
     
       7. The system of  claim 6 , wherein the region of interest ROI is circularly symmetric around a projection of the collimator rotation axis on the plane of the EPID. 
     
     
       8. The system of  claim 1 , wherein the processor is further configured to determine radiation beam tilt relative to the collimator rotation axis using the calculated asymmetry value, and further configured to initiate alignment of the radiation beam in the radiation device based on the determined radiation beam tilt. 
     
     
       9. A radiation treatment system, comprising:
 a radiation source configured to emit a radiation beam onto a collimator; the collimator being configured to rotate around a collimator rotation axis so as to generate a first scatter aperture in the radiation beam at a first location of the collimator, and a second scatter aperture at a second, symmetric location of the collimator; 
 an imaging device configured to measure radiation scattered from the first and second scatter apertures; and 
 a processing device configured to calculate a radiation beam asymmetry value based on the measured scattered radiation, 
 wherein the measuring of the scattered radiation includes measuring the scattered radiation using pixels of the imaging device positioned in the same region of interest ROI of the imaging device for each of the first and second scatter apertures. 
 
     
     
       10. The system of  claim 9 , wherein the first and second scatter apertures are generated by creating an off-axis field using the collimator and rotating the collimator around the collimator rotation axis from a first collimator location to a second collimator location, the second collimator location being rotationally symmetric to the first collimator location. 
     
     
       11. The system of  claim 10 , wherein the off-axis field is generated by positioning at least an element of the collimator so as to be offset relative to the collimator rotation axis, and wherein the generated off-axis field is a 1-2 cm rectangular or square radiation field. 
     
     
       12. The system of  claim 10 , wherein the imaging device is an electronic portal dose imaging device (EPID), and the scattered radiation is measured using a plurality of pixels located in the region of interest ROI of the EPID. 
     
     
       13. The system of  claim 12 , wherein the region of interest ROI is circularly symmetric around a projection of the collimator rotation axis on the plane of the EPID. 
     
     
       14. The system of  claim 9 , wherein the processor is further configured to determine radiation beam tilt relative to the collimator rotation axis using the calculated asymmetry value, and further configured to initiate alignment of the radiation beam in the system based on the determined radiation beam tilt. 
     
     
       15. A non-transitory computer-readable storage medium upon which is embodied a sequence of programmed instructions for determining radiation beam symmetry in a radiation therapy system, and a computer processing device which executes the sequence of programmed instructions to cause the computer processing device to:
 generate a first and a second, symmetric scatter aperture in the radiation field; 
 illuminate the first and the second scatter apertures with radiation; measure the radiation scattered from the first scatter aperture and the scattered radiation from the second scatter aperture; and 
 calculate an asymmetry value from the measured first and second scattered radiation. 
 
     
     
       16. The non-transitory computer-readable storage medium of  claim 15 , wherein the first and second scatter apertures are generated using a collimator of the radiation therapy system, the collimator being configured to rotate around a collimator rotation axis. 
     
     
       17. The non-transitory computer-readable storage medium of  claim 16 , wherein the first and second scatter apertures are generated by creating an off-axis field using the collimator and rotating the collimator around the collimator rotation axis from a first collimator location to a second collimator location, the second collimator location being rotationally symmetric to the first collimator location. 
     
     
       18. The non-transitory computer-readable storage medium of  claim 17 , wherein the off-axis field is generated by positioning at least an element of the collimator so as to be offset relative to the collimator rotation axis, the generated off-axis field being a 1-2 cm rectangular or square radiation field. 
     
     
       19. The non-transitory computer-readable storage medium of  claim 18 , wherein the scattered radiation is measured using a plurality of pixels located in a region of interest ROI of an imaging device, the region of interest ROI being circularly symmetric around a projection of the collimator rotation axis on the plane of the imaging device. 
     
     
       20. The non-transitory computer-readable storage medium of  claim 19 , wherein the computer processing device determines radiation beam tilt relative to the collimator rotation axis using the calculated asymmetry value, and aligns the radiation beam based on the determined radiation beam tilt.